The development of microminiature mechanical devices has advanced generally by use of a technique known as micromachining or microfabrication. See for instance, the discussion of microfabrication of mechanical devices by Angell et al. in "Silicon Micromechanical Devices," Scientific American, (April 1983), pp. 44-55. For example, a microactuator may comprise part of a microminiature valve used to control the flow of a carrier gas through a capillary column in a gas chromatograph. The microactuator may be required to open or close a fluid passage by displacing a moveable member (typically a moveable membrane, diaphragm, or boss) against a pressure of 200 pounds per square inch (1375 kilopascals), through a distance of as much as 100 micrometers.
Typically, applied power from an external source is provided to the microactuator, which employs one of various techniques to convert the applied power to an actuating force. Such microactuators can be considered as being actively-driven. Often the applied power is driven by a solenoid or gas pressure, or an electrical transducer that converts applied electrical power to thermal power. For example, an array of micromachined bi-metallic legs has been employed to provide a thermally-driven actuating force in a microminiature valve. As the bimetallic legs are heated, stresses are generated in the structure to deflect a protruding boss adjacent to an orifice, increasing or decreasing the flow of fluid to an attached fluid-bearing system.
The performance of the microminiature valve is determined in large part by its ability to operate in high temperature environment. If the thermal environment for the microminiature valve due to its surroundings is high, the microminiature valve will require a compliant diaphragm that effects suitable valve operation yet withstands the high temperature environment. Prior art approaches have employed a valve having a diaphragm that includes a valve seat etched in a silicon wafer and a flexible polymer valve diaphragm. The polymer diaphragm microminiature valve operating temperature limit is about 110.degree. C. A higher operating temperature limit is desired.
Hence, prior art approaches have not sufficiently attended to the degradation of the typical microminiature valve during exposure to high temperatures. A microminiature valve capable of operating in a high-temperature environment is accordingly desirable for use in for use in, for example, analytical instrumentation such as gas chromatographic instruments. In particular, an instrument with an injector that incorporates the high temperature microminiature valve can analyze samples containing higher-boiling sample components than an instrument with an injector that incorporates a valve of conventional design.